Chemical method of injecting water shut-off agent in air drilling



3,141,513 -OFF July 21, 1964 G. T. DAVIS CHEMICAL METHOD OF INJECTING WATER SHUT AGENT IN AIR DRILLING 3 Sheets-Sheet 1 Filed April 12, 1962 FIG.

FIG. 2

GEORGE THOMAS DAVIS INVENTOR.

July 21, 1964 DAVIS 3,141,513

CHEMICAL METHOD OF INJECTING WATER SHUT-OFF AGENT IN AIR DRILLING Flled April 12, 1962 3 Sheets-Sheet 2 DILUTED WITH 40 WATER L20 0 RESIN AS RECEIVED- \A O GEL TIME AT 25 C. HRS

l l l l l l l l l l l WT."/ Fe Gig- 0 0.4 0.8 L2 L6 2 O 2.4 2.8 3.2 3-6 4.0 4.4

pH-- 2.45 2.03 L82 BASED ON PLASKON BEFORE DILUTION FIG. 3 UREA-FORMALDEHYDE POLYMER (PLASKON 5395) FOR QUICK-SETTING PACKER GEORGE THOMAS DAVIS INVENTOR.

AGENT July 21, 1964 G T DAV AGENT IN AIR DRILLING Filed April 12, 1962 LIG- DENSITY OF MIXTURE GM/CC.

'-' cc| TO PLEOGEN IOOO I I I 35 40 I l I I I O 5 IO I5 3O IS CHEMICAL METHOD OF INJECTING WATER SHUT-OFF 5 Sheets-Sheet 3 CC. OF DILUENT ADDED TO lOO GRAMS OF RESIN FIG. 4 DENSITY OF STYRENE-POLYESTER AND UREA-FORMALDEHYDE RESINS CAN BE ADJUSTED TO DESIRABLE RATIO GEORGE THOMAS DAVIS INVENTOR.

AGENT United States Patent of Delaware Filed Apr. 12, 1962, Ser. No. 187,006 7 Claims. (Cl. 175-72) This invention is directed to a method for sealing a porous interval of a wellbore wall. It is also concerned with an improved method of drilling earth boreholes by rotary drilling wherein a gas rather than a liquid is employed as the circulation medium for lifting cuttings to the surface. Specifically, the invention is concerned with a method for sealing off formation Water encountered while air drilling.

In its broadest aspect, the invention includes the steps of introducing a sealing agent into a wellbore opposite a porous interval to be sealed, introducing a delayed-action in-situ pressure source opposite said porous interval, and then confining the sealing agent and the pressure source opposite said porous interval for a time suflicient to permit the pressure developed to force at least a portion of the sealing agent into the pores of the confined interval, thereby sealing it.

In a more limited embodiment, the method involves the steps of interrupting a rotary air drilling procedure when the influx of water into the borehole becomes excessive, then introducing a sealing agent itno the borehole beneath a quick-setting resin packer which floats on the sealing agent and then solidifies without shrinking. A delayedaction pressure source is introduced with the sealing agent whereby a pressure is generated in-situ after the solidification of the packing agent, thereby forcing the sealing agent into the pores of the water-producing formation. The drilling procedure is resumed after the sealing agent has sufiiciently cured to prevent further influx of water.

The term air drilling as used herein refers generically to the use of any suitable gas or gaseous mixture as a circulation fluid, although air or natural gas is usually employed. The advantages of air drilling compared with the more conventional use of liquid drilling fluids include a higher penetration rate, longer bit life, and a cleaner borehole. A borehole uncontaminated by drilling mud is desirable because it facilitates the detection of oil bearing formations and also improves the productivity of a completed well.

A major problem, however, which detracts somewhat from the above advantages is the reflux of formation water encountered while drilling. The water causes a conglomeration of bit cuttings which interferes both with the action of the drill bit and with the circulation of air within the borehole. Moreover, if excessive amounts of water invade the borehole the hydrostatic head may become great enough to prevent air circulation altogether and thereby force an abandonment of air drilling and a conversion to liquid drilling fluid.

Prior art methods of formation water shut-off have required first of all that the water-producing formation be isolated from the remainder of the borehole by expanding a rubber sleeve packer against the wall of the hole, followed by the injection of a sealing agent from the surface and forcing the sealing agent into the pores of the formation by pressure applied from the surface of the ice earth. Too frequently, the mechanical packer cannot form a perfect seal against the borehole Wall with the result that water shut-off is incomplete. Moreover, the sealing agent may solidify prematurely, resulting in a stuck drill stem. The installation of a mechanical packer is a costly and time consuming step. The method of this invention avoids such expense and also avoids the risk of sticking the drill stern, while at the same time assures a more perfect seal.

The first step of the invention is the interruption of gas circulation upon encountering excess formation water. Accordingly, the operator must be able to recognize the symptoms of water influx into the borehole. One such indication is a diminished return of dust and cuttings at the blow line or exhaust pipe. The change may be gradual or abrupt depending primarily upon the rate of water influx. It is possible, however, that a return of dust and dry cuttings may persist even though a wet formation is being traversed. This is due to erosion and abrasion from dry uphole sections caused by the drill string and by the air stream itself. A simple test for a water formation is to hold some dry object in the path of the blow line return and to notice any accumulation of moisture or wet dust.

Another, more serious indication of having drilled into water is the circulation pressure. Wet cuttings ball up at the bit and also bridge the well bore causing an increased and erratic circulation pressure. Any accumulation of water in the borehole also increases circulation pressure because of its hydrostatic head.

Next, a sealing agent containing expansible capsules is introduced into the bottom of the borehole opposite the water-producing formation. A preferred sealing agent is Pleogen 1000 manufactured by Mol-Rez Division of American Petrochemicals Co., Minneapolis, Minnesota. This material is an unsaturated polyester-styrene prepolymer, the setting time of which can be suitably controlled by the addition of a diluent, and by the addition of variable quantities of tertiary butyl peroxide and cobalt naphthenate, or other polymerization catalysts. The density of the sealing agent is adjustable by the choice and amount of diluent in order to ensure that the sealing agent is more dense than other fluids contained in the borehole and will therefore remain opposite the water producing formation. Carbon tetrachloride is an example of a suitable diluent. However, the invention is not limited to the use of Pleogen 1000 as the sealing agent since any prepolymer solution generally satisfying these conditions is useful in the method of the invention. Other sealing agents include epoxy resins, which may be cured with a diamine catalyst; polymethyl methacrylate cured with peroxides; and phenol-formaldehyde resins cured with acids or bases.

The expansible capsules introduced with the sealing agent operate to provide a delayed-action in-situ source of pressure for forcing the sealing agent into the pores of the water producing formation. The capsules contain in separate compartments two chemicals which will react when mixed to generate a gas. The chemicals are kept separated in order to delay the pressure action by a soluble clamp placed about the central portion of the capsule. Lucite is an example of a soluble plastic which is used as a clamp about the capsule. The polyester-styrene prepolymer is typically added as a solution in excess styrene. The styrene acts to slowly soften and dissolve the clamp, after the setting of a packer thereabove, permitting the chemicals to mix and react to produce a gas, thereby generating the necessary pressure to force the sealing agent into the water producing formation.

The chemical packer is then introduced. It is a liquid, quick-setting resin composition which floats on the sealing agent and then solidifies without shrinking. Plaskon 5395, manufactured by the Barret Division of Allied Chemical and Dye Corp, is an example of such a packing material. It is an aqueous urea-formaldehyde prepolymer, characterized by negligible shrinkage upon further polymerization, as well as by virtually no temperature increase associated with rapid curing. These properties ensure a good packing operation above the sealing agent. The setting time is controlled by the pH as shown in detail below.

Soon after the packing material has solidified to form a firm plug in the borehole, the soluble clamp on the capsules contained in the sealing agent is dissolved by the unpolymerized sealing agent, or by the solvent added therewith, if necessary, thereby releasing the chemicals which react, causing the capsules to expand thereby raising the pressure exerted by the sealing agent against the borehole wall. Once the capsules have expanded to the limit that conditions will permit, the system is left undisturbed until the sealing agent fully cures in the pores of the water producing formation, whereupon drilling is resumed. The packer and the excess sealing agent are not a serious obstruction in the borehole, since they are readily drillable.

The entire sequence of steps may be carried out without removing the drill string from the borehole. The only limitation imposed on the method by simply lifting the bit above the interval to be sealed off, relates to the size of the capsules introduced with the sealing agent. That is, the capsules must be small enough to pass through a bit nozzle. This feature of the method is not to be construed as limiting the scope of invention, however, since larger capsules may be employed in the event that the drill string is removed from the hole.

A detailed description of the invention is provided by reference to the accompanying drawings.

FIGURE 1 is a cross-sectional view of the earth, showing a borehole and a water-producing formation which it is desired to seal off.

FIGURE 2 is an elevational view of an expansible capsule for use in generating pressure in accordance with the invention.

FIGURE 3 is a graphic presentation of the gel time of Plaskon 5395 versus the weight percent of ferric chloride added to control the pH and thus the gel time.

FIGURE 4- is a plot of density versus volume of diluent added to Pleogen 1000 and Plaskon 5395, respectively.

Referring now to FIGURE 1, borehole 11 is surrounded by water-producing formation 12 which has forced an interruption of air drilling. Sealing agent 13 is introduced beneath quick-setting resin packer 14. After packer 14 solidifies, the soluble plastic clamp 15 on expansible capsule 16 is dissolved away, thus permitting the chemical reactant contained in the separate halves of the capsules to mix, whereby a gas is generated thereby forcing the sealing agent 13 into the pores of water-producing formation 12.

As represented by FIGURE 1, the preferred circumstances for conducting a seal-off in accordance with the invention arise from having interrupted drilling immediately below the water-producing formation, whereby the sealing agent may conveniently be suported by the hole bottom. Unfortunately, it is not always possible by current techniques to detect an offending aquifer im mediately upon its penetration. Accordingly, in the event that drilling has progressed considerably beyond the water-producing formation before interruption is forced, the method of the invention can nevertheless be carried out by placing a conventional drillable packer below the level of water influx to serve in the same capacity as would the hole bottom under more favorable circumstances.

Referring now to FIGURE 2, an enlarged view of an individual capsule 16 is shown which includes soluble plastic clamp 15 and expansible member 18. As a preferred example, the soluble plastic clamp 15 may be made of polymethyl methacrylate, known commercially as Lucite or Plexiglas. Other examples of soluble clamp materials include polystyrene, epoxy resins, and nylon. These materials are not necessarily equivalent, however. A suitable solvent must be chosen which will dissolve the particular clamp material. The expansible or inflatable member 18 is made of solvent-resistant material such as Neoprene, polyethylene film, polypropylene film, or other inflatable material.

Examples of readily available chemicals which interact to generate a gas are sodium bicarbonate and hydrochloric acid to produce carbon dioxide; sodium and water to produce hydrogen; calcium hydride and water to produce hydrogen; calcium carbide and water to produce acetylene.

Referring now to FIGURE 3, a curve is shown which demonstrates the facility with which the gel time of Plaskon 5395 is controlled by adjusting the pH. FeCl is only an example of a material which may be added to lower the pH. The commercial product is a 65% ureaformaldehyde prepolymer in water which undergoes further polymerization or curing under acidic conditions. The material sets with negligible exotherm even in large batches, and exhibits very little shrinkage. It can be cured rapidly at normal borehole temperatures.

Referring now to FIGURE 4, the curves shown illustrate that the styrene-polyester and urea-formaldehyde resins can be adjusted to the proper density whereby the Plaskon floats on the Pleogen as shown in FIGURE 1. For example, the addition of 35 cc. of diluent to gms. of each of the respective resin compositions provides a system wherein the sealing agent has a density of about 1.25, and the quick-setting packer a density of about 1.21, thus ensuring the proper density ratio.

What is claimed is:

1. A method for sealing a porous interval of a wellbore wall which comprises introducing a sealing agent into said wellbore opposite said porous interval, introducing a delayed action in-situ pressure source opposite said porous interval, said pressure source comprising at least one expansible container divided by a soluble clamp into separate sections, said separate sections containing chemical reagents which react when mixed to generate a gas, and confining said sealing agent and said pressure source opposite said porous interval for a time sufficient to permit said pressure source to force at least a portion of said sealing agent into the pores of said interval, thereby sealing said porous interval.

2. In a process for the rotary air drilling of a borehole in the earth, the improved method of operation upon encountering a water-producing formation which comprises introducing a sealing agent into said borehole opposite said water-producing formation, introducing a delayed-action in-situ pressure source opposite said formation, isolating said sealing agent and said pressure source from the remainder of said borehole, and resuming the drilling operation after a time suflicient to permit said pressure source to force at least a portion of said sealing agent into said water-producing formation and sufiicient to permit a portion of said sealing agent to solidify within said formation.

3. A process as defined by claim 2 wherein said sealing agent comprises a synthetic prepolymer solution.

4. A process as defined by claim 2 wherein said sealing agent comprises a styrene-polyester prepolymer solution.

5. A process as defined in claim 2 wherein said delayed action in-situ pressure source comprises at least one expansible container separated into two sections by a soluble clamp and wherein said separate sections contain chemical reagents which react when mixed to generate a gas.

6. A process as defined by claim 2 wherein said sealing agent and said delayed-action pressure source are isolated within said borehole by introducing a quick-setting resin prepolymer solution into said borehole, said quicksetting prepolymer solution being of a density somewhat less than that of said sealing agent whereby said quicksetting resin prepolymer floats thereon.

7. A process as defined by claim 6 wherein said quick- 6 setting resin prepolymer solution comprises a urea-formaldehyde prepolymer.

References Cited in the file of this patent UNITED STATES PATENTS 1,843,002 Small Jan. 26, 1932 2,527,581 Searer et a1. Oct. 31, 1950 2,836,555 Armentrout May 27, 1958 2,867,278 Mallory et a1. Jan. 6, 1959 3,011,547 I-lulbert et al. Dec. 5, 1961 3,027,943 Reistle Apr. 3, 1962 3,087,544 Forsman Apr. 30, 1963 

2. IN A PROCESS FOR THE ROTARY AIR DRILLING OF A BOREHOLE IN THE EARTH, THE IMPROVED METHOD OF OPERATION UPON ENCOUNTERING A WATER-PRODUCING FORMATION WHICH COMPRISES INTRODUCING A SEALING AGENT INTO SAID BOREHOLE OPPOSITE SAID WATER-PRODUCING FORMATION, INTRODUCING A DELAYED ACTION IN-SITU PRESSURE SOURCE OPPOSITE SAID FORMATION, ISOLATING SAID SEALING AGENT AND SAID PRESSURE SOURCE FROM THE REMAINDER OF SAID BOREHOLE, AND RESUMING THE DRILLING OPERATION AFTER A TIME SUFFICIENT TO PERMIT SAID PRESSURE SOURCE TO FORCE AT LEAST A PORTION OF SAID SEALING AGENT INTO SAID WATER-PRODUCING FORMATION AND SUFFICIENT TO PERMIT A PORTION OF SAID SEALING AGENT TO SOLIDIFY WITHIN SAID FORMATION. 